Food products and the like are commonly mixed and blended under commercial conditions in vessels which are more or less cylindrical in horizontal or vertical section and provided with a power driven agitator or agitators which rotate therein. The vessels are heated or cooled as desired. The contents are often of a nature which sticks to the interior vessel walls. While the agitators scrape off such materials to a considerable extent, the vessel walls are not always truly circular and of course there must be some clearance between agitator and wall. Various types of scrapers have been suggested but none has achieved any substantial commercial acceptance because of the tendency to leave material on the walls, which if heated will cause the material to overcook and even burn thereon. Overcooking and burning can have a very deleterious effect on product quality, especially flavor and odor. It also lowers the efficiency of the cooking operation and is often very difficult to remove.
A type of vessel suitable for large batches is horizontally elongated and has a pair of agitators which rotate on parallel horizontal shafts. The bottom of the vessel in vertical section is a pair of circular arcuate troughs meeting mid-way between the agitators in a cusp. The troughs have radii slightly greater than the radius of the agitators. Those trough walls merge at the sides of the vessel into vertical walls which extend to the top of the vessel. When the vessel walls are heated for hot mixing and blending, no scraper affixed to the agitators can scrape the vertical walls of the vessel and any material which is deposited on any heated vertical portion of the walls will usually burn there with all of the attendant disadvantages earlier described. Vessels of the type mentioned therefore are seldom used to the full extent of their capacity.